Improving corrosion resistance of Zn–5Al (wt%) alloy by microalloying with samarium

Abstract

The role of the rare earth element Sm in as-cast Zn–5Al alloy was studied in this work. A three times higher improvement than the control group on corrosion resistance was found with rare earth Sm adding (0.15 wt%). By using an electron prove micro analyzer (EPMA), focused ion beam (FIB) and scanning Kelvin probe force microscopy (SKPFM) techniques, two main mechanisms of the premium performance of the Sm adding were revealed. One was that the non-uniform nucleation and component undercooling induced by Sm adding, reduced the α-Al layer spacing thus improved the covering efficiency of the Al2O3 film. The other was that the dissolved Sm in the Zn/Al eutectic structure modulated the electron work function thus induced the attenuation of Volta potential discrepancy. The experimental results show that when the addition of Sm is 0.15 wt%, the minimum Volta potential difference between α-Al and η-Zn phases is achieved, and excessive or deficient Sm addition will increase the Volta potential difference.